Natural Rubber Foam for Modular Acoustic Pods: Comparative Acoustic Performance and Full-Scale Prototype Performance Assessment
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Abstract
This study investigated the acoustic performance of bio-based natural rubber foam (NR foam) relative to conventional acoustic materials for modular acoustic pod applications through laboratory-scale material screening and full-scale prototype performance assessment. The novelty of this work lies in the introduction of the proposed Normalized Acoustic Performance Index (NAPI), a study-specific composite metric developed to compare the balance between sound absorption and material-level sound transmission resistance, together with a system-level assessment of a full-scale acoustic pod incorporating NR foam. Five materials, including NR foam, polyester fiber, polyurethane (PU) foam, polystyrene (PS) foam, and coconut fiber, were evaluated using impedance tube methods for sound absorption coefficient (SAC) and sound transmission loss (STL). Among the five materials investigated and the selected normalization reference values, NR foam yielded the highest NAPI value of 0.58, indicating the most balanced combination of sound absorption and material-level sound transmission resistance among the tested specimens. A full-scale acoustic pod incorporating NR foam within the wall cavities was subsequently constructed and evaluated under field measurement conditions. The pod exhibited octave-band sound level differences ranging from 37.1 to 49.7 dB, with an arithmetic mean of 42.4 dB across 125–8000 Hz. These values represent the combined acoustic performance of the complete enclosure and do not isolate the individual contribution of the NR foam layer. The developed NR foam exhibited a bulk density of 0.4238 g/cm³, a compressive strength of 80 kPa, a flexible interconnected open-cell structure, and HBF classification under the horizontal burning test conditions employed. Overall, the findings demonstrate the potential of NR foam as a bio-based material providing a balanced combination of sound absorption and material-level sound transmission resistance for modular acoustic enclosure applications.
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